The present invention relates to granular detergent compositions which are excellent in powder characteristics (physical properties of granules) but are free from phosphorus. More particularly, the present invention relates to granular detergent compositions free from phosphorus which are improved in powder characteristics such as compression-caking and free flowability.
From the past, sodium tripolyphosphate has chiefly been used as a builder for granular detergents. Sodium tripolyphosphate is not only excellent in detergency-improving action but also effective to improve the powder characteristics of the resultant granular detergents and thus affords detergents with well balanced properties when used in combination with sodium sulfate as bulking agent.
In recent years, however, environmental pollution has become a big social problem and the use of such polyphosphates has been identified as one of the causes of water pollution and thus restricted in use considerably. For this reason, builders which were formerly only in limited use, such as carbonates, silicates or citrates, are being substituted in place of the polyphosphates.
However, granular detergents prepared by using these builders have disadvantages; they tend to become caked upon compression, thus incurring deterioration of important powder characteristics such as free flowability. In the industry of manufacturing granular detergents, therefore, there is a great demand for development of an auxiliary additive which can afford, without necessity of using polyphosphates, high detergency combined with powder characteristics comparable with the case of using polyphosphates.
As a result of extensive researches made for meeting such requirement, it has now been found that the powder characteristics as well as detergency are better improved as the amount of an alkali sulfate becomes smaller when a specific composition of an anionic surfactant is selected and the molar ratio x of a silicate in term of M.sub.2 O.xSiO.sub.2 wherein M stands for an alkali metal is also selected within the range of 2.5-3.6 in detergents containing builders comprising mainly silicates, carbonates and hydroxypolycarboxylates. The present invention is based on this finding.